1. Field of the Invention
The present invention relates generally to the field of occlusion of vessels and other tubular structures in the body. More particularly, it concerns a method and apparatus for repositionable, self-anchoring occlusion including vascular and ureter occlusion.
2. Description of Related Art
Percutaneous occlusion techniques have become indispensable tools in minimally invasive management of a wide range of pathological conditions. Use of permanent mechanical occlusion devices has been shown to be equivalent to that of surgical ligation. The Gianturco-Wallace stainless steel coil (Cook Inc., Bloomington, Ind.) has been the most widely used permanent, expandable intravascular occlusion device for transcatheter delivery (Gianturco et al., 1975). The use of detachable balloons, another effective mechanical occlusion technique, has been largely abandoned in the United States because of safety concerns (Sharaffiuddin et al., 1996).
Percutaneous coil embolization has been shown to be advantageous over traditional surgical procedures in treatment of life threatening hemorrhage due to trauma or obstetric emergencies (Schwartz et al., 1993; Teitelbaum et al., 1993; Selby Jr., 1992; Levey et al., 1991; Ben-Menachem et al., 1991; Vedantham et al., 1997). Furthermore, coils have been used alone or in combination with microvascular embolic agents for the treatment of vascular fistulas and malformations, tumors, and varices (Wallace et al., 1979; Hendrickx et al., 1995; Furuse et al, 1997; White et al., 1996; Sagara et al., 1998; Punekar et al., 1996). During the last few years, the transcatheter closure of the patent ductus arteriosus (PDA) with coils has become a frequently used technique (Hijazi and Geggel, 1994; Hijazi and Geggl, 1997).
Although coil type occlusion devices have shown at least a degree of utility, they have a number of drawbacks that could be significant in some applications. Intravascular stability of the coils has been shown to be highly dependent on proper matching of coil diameter with the diameter of the target vessel (Nancarrow et al., 1987), and with the exception of small vessels, a single coil rarely results in a stable occlusive thrombus (Hijazi and Geggel, 1994). Moreover, a long vascular segment is often obliterated because of the frequent need for multiple coils and the coils often remain elongated within the vessel because their unconstrained diameter is larger than the vascular lumen. Furthermore, delayed recanalization rates of 37%-57% have been reported in humans within 1-3 months after initially successful coil embolization (Sagara et al., 1998; O'Halpin et al., 1984; Schild et al., 1994).
These and other drawbacks have inspired modifications in the design and technique of coil embolization. Recently, detachable microcoils and macrocoils with controlled delivery have been designed to achieve a more compact conglomerate of the coil and to prevent migration by allowing optimal positioning of the coil before release (Zubillaga et al., 1994; Guglielmi et al., 1995; Marks et al., 1994; Reidy and Qureshi, 1996; Uzun et al., 1996; Tometzki et al., 1996; Dutton et al., 1995). However, since optimal arrangement of the coil alone may not prevent migration in some cases, such as high flow conditions or venous placement, a coil anchoring system has been devised (Konya et al., 1998). Although an anchoring system may stabilize a coil conglomerate within the vasculature, significantly reducing or eliminating the possibility of coil migration, such a system may render the coil non-repositionable.
Several different non-coil devices have been designed to achieve a more stable, limited size plug with higher hemostatic efficiency particularly for transcatheter closure of larger vessels (Schmitz-Rode et al., 1993) and PDAs (Pozza et al., 1995; Magal et al., 1989; Grifka et al., 1996). Recently, initial clinical experiences with a new mesh PDA occluder have been reported (Sharafuddin et al., 1996; Masura et al., 1998). A similar self-expanding, repositionable quadruple-disc device constructed of a braided nitinol mesh and polyester fibers has been reported to be superior to standard Gianturco coils in experimental occlusion of mid-size arteries (Sharaffuddin et al., 1996).
Although such non-coil devices may be repositionable, they too exhibit drawbacks. For instance, the quadruple-disc device is several centimeters long in an elongated fashion, making difficult to keep the superselective position of the catheter tip during deployment. Although the mesh-PDA occluder has demonstrated utility, its proper placement requires a proper match both in size and shape between the occluder and the lesion to be occluded. A common disadvantage of both designs is that they lack guidewire compatibility. As a result, a delivery catheter must often be navigated to the site of occlusion first before an occluder may be loaded into the catheter and delivered through it. Another relative disadvantage of both devices is their cost of manufacturing.
Percutaneous catheter technique for permanent closure of isolated persistently patent ductus arteriosus (PDA) is now a treatment of choice among doctors, obviating open surgery. The configuration of the PDA varies considerably. A majority of PDAs tend to have a funnel or conical shape due to ductal smooth muscle constriction at the pulmonary artery insertion, although narrowings in the middle or aortic ends can be observed (Krichenko, 1989). That is the reason why not only the size, but also the configuration, of the lesion plays a significant role in selecting an appropriate occluding device. Except from the small caliber lesions (with a maximum diameter of 2.5 mm or 3.3 mm, respectively), where some authors have achieved successful closure of the PDA with Gianturco coils (Cambier, 1992; Lloyd, 1993; Sommer, 1994), Rashkind's “double umbrella” occluder is the most often used device for this purpose (Rashkind, 1987; Hosking, 1991; Latson, 1991; Wessel, 1988; Report of the European Registry, 1992). It is available in two sizes (with a diameter of 12 mm and 17 mm) which require a 8-P and 11-F delivery system, respectively.
In the majority of cases, the deployment of the traditional PDA device is performed from a femoral vein access (Report of the European Registry, 1992). Because of the size of the delivery sheath, such a device is not suitable for the treatment of patients with a body weight of less than 8 kg. Using even a larger umbrella, this procedure is not recommended for the treatment of the lesions with a diameter of 8 mm or above (Latson, 1991). About 80% of unselected patients with isolated PDA are candidates for the Rashkind device using the aforementioned criteria (Latson, 1991). With the Rashkind device, the proportion of patients with residual flow through the lesion fell from 76% immediately after implantation to 47% by the day after implantation and to 17% by a year after implantation (Report of the European Registry, 1992). According to some authors the residual flow carries a potential risk of infective endocarditis and should be avoided if possible. Its abolishment can be achieved by implantation of another device or surgery.
One of the main drawbacks of the Rashkind umbrella is that it is not suitable for occlusion of all types of PDA. Preferably, it is used to occlude short PDAs with relatively wide end-openings. Its two discs cover both the pulmonary and the aortic opening of the PDA. Longer PDA may hinder the discs to be positioned in the proper way, that is, parallel to each other, thereby deteriorating its self-anchoring. Another disadvantage of the umbrella is that the occluding capacity of the design depends exclusively on the thrombogenicity of the porous Dacron material, frequently resulting in partial and lengthy occlusion.
For the majority of patients with urinary leakage and/or fistlas (mainly due to tumor propagation to their ureters), the diversion of urine is currently performed by a percutaneous transrenal approach together with ureteral occlusion. Formerly, detachable and non detachable balloons were used for this purpose, but they did not cause satisfactory ureteral occlusion. Migration as well as deflation of the balloons occurred relatively frequently (Gunter, 1984; Papanicolau, 1985) leading to recurrence of the urine leakage. A silicone ureteral occluder was developed and used with only limited success because of device migration (Sanchez, 1988). This resulted in repositioning and consequent incomplete ureteral occlusion. It appears that the best results have been accomplished with Gianturco coils and Gelfoam embolization (Bing et al. 1992 a; ). Even with multiple coil placements, together with Gelfoam plugs, the ureteral occlusion may sometimes be achieved for only weeks or months, and was attributed mostly to the induced urothelial hyperplasia (Bing et al., 1992 b). Coil migration was frequently encountered in these studies. The lack of appropriate self-anchoring results in coil migration which eventually deteriorates the occlusive effect.
Problems pointed out in the foregoing are not intended to be exhaustive but rather are among many that tend to impair the effectiveness of previously known occlusion systems. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that previous techniques appearing in the art have not been altogether satisfactory, particularly in providing fast, non-migratory, self-anchoring, repositionable occlusion.